1. Field of the Invention
The present invention relates to a defect inspection apparatus which applies illumination light to a sample such as a semiconductor wafer or a glass substrate of a flat display (FPD), and picks up an image of the light from the sample at this moment to perform defect inspection of the sample from image data thereof.
2. Description of the Related Art
Generally, in the middle of a manufacturing process of, for example, a semiconductor wafer or a glass substrate of a flat display, such as a manufacturing process having a photolithography process, there is a formation in which a patterned resist is provided on a substrate made of a silicon or glass plate via a film forming layer. However, in the photolithography process, if the resist applied to a substrate surface has an uneven film or dust sticking thereto, the uneven film or dust causes such defects as an irregular line width of the pattern or pin holes in the pattern after etching.
Under these circumstances, in the manufacturing process of the substrate before etching, all substrates are usually subjected to an inspection for finding the presence of the above defects. A method adopted to the total inspection often includes visual observation of all the substrates by operators. However, a difference of judgment of the operators dependent on experience and considerable effects of the dust made by the operators themselves in a clean room have led to a method in which the operators and the substrates are separated as far as possible to conduct observation, or a method which provides an apparatus with a judging function.
FIG. 16 is a diagram showing a configuration of a conventional defect inspection apparatus described in Jpn. Pat. Appln. KOKAI Publication No. 9-61365. An illumination section 2 and an image pickup section 3 are provided above a sample 1. The illumination section 2 applies illumination light to the sample 1 at an incidence angle θ0, and a collimator lens 4 is disposed in its light path and forms the illumination light from the illumination section 2 into a parallel light flux.
The image pickup section 3 is provided at a position opposite to the illumination section 2 with reference to a normal line n, and is disposed at an angle θ0 to the sample 1. The image pickup section 3 has a line sensor camera 5 and an image formation lens 6. A collimator lens 7 is disposed between the image pickup section 3 and the sample 1.
With such a configuration, a light flux, which is output from the illumination section 2 and diffused, is formed into the parallel light flux by the collimator lens 4 and gives line illumination to the sample 1. The light reflected on a surface of the sample 1 is incident upon the image formation lens 6 through the collimator lens 7, and is formed as an image of the surface of the sample 1 on an image pickup surface of the line sensor camera 5. Image data obtained by the image pickup with the line sensor camera 5 is then subjected to image processing, so as to perform the defect inspection of the surface of the sample 1.
In the manufacturing process having the photolithography process described above, when the resist is applied to the surface of the sample 1, the applied resist goes around to a rear surface of the sample 1 to, for instance, cause peripheral portions of the rear surface to bulge. However, under a current situation, even when the peripheral portions of the rear surface of the sample 1 bulge, or the rear surface of the sample 1 has flaws or dust sticking thereto, it is difficult to take measures for these problems because a technique described in the above-mentioned publication does not provide means to detect the rear surface of the sample.